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Transport in Plants
Have you visited or at least heard about
the giant California redwoods? These
amazing trees can grow up to 100 m
tall! In Alberta, even the trees in the
central and north central regions of the
province consist of tall aspens that can
reach heights of up to 25 m.
How do trees like the California
redwoods and the aspens of Alberta get
water and minerals from their roots to
their leaves way up at the top?
Turn to page 315 of the textbook and
read the introductory paragraphs of
“Transport in Plants.”
1. Name three plant structures involved
in the movement of water and other
materials in plants.
Check
Check your answer with the one on page 131.
In the next activity you will observe how
water clings to the surface of a solid.
Science 10 • Module 3 • Section 3
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123
QuickLab
Capillary Action
Read the entire activity on page 315 of the textbook.
If you have access to a supervised laboratory, do Part A. If you do not have
access to a supervised laboratory, do Part B.
Part A
Follow the steps outlined in the procedure on page 315 of the textbook.
Step 1
Step 2
Step 3
2. Answer questions 1 to 5 of “Questions.”
Check
Check your answers with those on pages 131 and 132.
Part B
Complete steps 1 and 3 of the procedure on page 315 of the textbook. For step 1,
you can use your finger to add one drop of water at a time to a penny. For step 3,
if you are cutting a stem from a house plant, cut only a small stem with a single
leaf. Be sure to check if it is okay for you to cut a part of the plant if the plant is
not yours.
Pay careful attention when cutting stems.
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The following diagram shows the observations made by a student who
performed step 2 of the procedure.
Step 2: Capillary Tubes
beaker
water level
in tubes
water and
food colouring
Use the preceding information and your results in steps 1 and 3 to answer
question 2 in Part A.
In the preceding activity you saw that water droplets
cling to themselves and to the surface of a penny.
Scientists have different names for the attraction of liquid
molecules to each other and to other surfaces.
For more information, turn to page 316 of the textbook
and read “Cohesion and Adhesion.”
3. What is cohesion?
4. What is adhesion?
5. Do you think plants would be able to draw soapy water up the stem? Explain.
Check
Check your answers with those on page 132.
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125
Other ways through which water moves up the stem to the leaves in plants are
root pressure and transpiration pull. Roots draw water and minerals from
the soil. This creates a greater pressure in the roots than there is in the stem and
leaves, thus forcing the water up the stem. Transpiration pull results from the
evaporation of water through the leaves. This creates a pull on the water within
the stem and leaves.
Turn to pages 316 to 318 of the textbook and read “Root Pressure” and “From
Root to Leaf: Water Transport in Plants.”
6. What evidence is there that root pressure occurs?
root pressure:
pressure exerted
on water in the
roots by osmosis
transpiration
pull: a pull on
water molecules
in xylem due to
the evaporation
of water
through
stomata and
lenticels
7. Through what process is water drawn into the roots?
8. How does transpiration pull work to move water up the stem of a plant?
9. How does temperature affect transpiration pull?
10. Closely study Figure C3.19 on page 317 of the textbook. Then answer
questions 1 to 4 of “Minds On . . . Colourful Carnations.”
11. Carefully study Figure C3.20 on page 318 of the textbook. Name the
processes involved at each of the following locations that help to move water
from the ground up through the stem to the leaves and out into the air.
a. root system
Check
tonicity:
a term that
relates the
concentration of
solute particles
in solutions
separated by a
semi-permeable
membrane
b. stem
c. leaves
Check your answers with those on page 132.
In the next activity you will observe the effect of concentration of solute particles
on plant cells. The concentration of solute particles in solutions separated by a
semi-permeable membrane is referred to as tonicity.
COPYRIGHT © UNIVERSITY OF ARKANSAS AT LITTLE ROCK. ALL RIGHTS RESERVED.
Figure 2.4: Elodea leaf cells
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Inquiry Lab
Tonicity and Plant Cells
Read the entire activity on page 319 of the textbook.
12. Predict the effect of increased tonicity of the environment on plant cells.
Check
Check your answer with the one on page 133.
If you have access to a supervised laboratory, do Part A. If you do not have
access to a supervised laboratory, do Part B.
Part A
Follow steps 1 to 6 of the procedure outlined on page 319 of the textbook. Pay
special attention to the safety precautions mentioned.
13. Do the following as you complete the procedure.
a. Draw a diagram of the field of view of Elodea leaf cells, and calculate
the size of Elodea leaf cells (step 3).
b. Describe the movement of material around the cell and into and out of
the cell (step 4).
c. Describe the changes in the cell structures after adding the salt solution
(step 6).
14. Answer the following on page 319 of the textbook.
a. questions 1 to 4 of “Analyzing and Interpreting”
b. question 5 of “Forming Conclusions”
Check
Check your answers with those on pages 133 and 134.
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Part B
The following is a diagram of Elodea leaf cells drawn by a student who observed
them using a microscope with a total magnification of 400¥.
Field of View at 400x
Elodea leaf cell
chloroplast
15. Use the diagram of Elodea leaf cells under 400¥ to calculate the actual size
of an Elodea leaf cell in micrometres (µm). Assume the field diameter of a
microscope with a total magnification of 40¥ to be 4.5 mm.
Check
Check your answer with the one on page 134.
Insert the Science 10 Multimedia CD into your computer, and view the segment
“Cytoplasmic Streaming in Elodea Cells.” In this segment you will get a
close-up view of the cytoplasmic streaming in an Elodea leaf cell.
16. What observations can you make about cytoplasmic streaming in Elodea
leaf cells?
Check
Check your answer with the one on page 134.
Cut a leaf from a healthy plant. Observe the shape of the leaf and how it holds
its shape. Immerse the leaf for about two minutes in a salt solution made with
about 5 mL of table salt in 100 mL of water. Remove the leaf and lay it down
on a paper towel to absorb excess moisture.
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17. a. Pick up the leaf and observe its shape and how it holds its shape.
Record your observations.
b. What do you think happened to the leaf to cause the change?
18. What term is used to describe the salt solution relative to the leaf’s cell
contents?
Check
Check your answers with those on page 134.
Turn to page 320 of the textbook and read “The Effect of Tonicity on Plant Cells.”
Study the photographs in Figure C3.21 closely.
19. a. Describe plasmolysis.
b. What is the effect of plasmolysis on a leaf of a plant?
20. What happens to a plant that has been in a salt solution for a few minutes
when it is returned to fresh water?
21. Why is turgidity important to green plants?
Check
Check your answers with those on page 134.
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In addition to water, plants need a supply of food (sugars) to survive. Xylem and
phloem cells are the mechanism for transport of sugars throughout the plant.
Read “From Source to Sink: Sugar Transport in Plants”
on pages 320 and 321 of the textbook. Study Figure
C3.22 on page 321 carefully.
22. Why are xylem and phloem cells important to the
survival of the plant?
23. What terms are used for where sugars are
manufactured and where they are used or stored?
24. Describe the mechanism by which the sugars are
moved from the leaves to the rest of the plant.
25. What are the sugars used for when they are passed on to the rest of the plant?
26. How is the constant flow of sugar and water down the phloem maintained?
Check
Check your answers with those on pages 134 and 135.
Looking Back
You have just completed the concepts
for this lesson. You identified a number
of factors and processes involved in the
movement of water and sugars in plants.
27. Answer questions 1, 2, 3, and 9 of “Check and Reflect” on page 322 of the
textbook.
Check
Go to ...
130
Check your answers with those on page 135.
Go to pages 5 to 7 of Assignment Booklet 3C and complete questions 20 to 28.
Science 10 • Module 3 • Section 3
Copyright © 2005 Alberta Education
Glossary
adhesion: the tendency of unlike molecules to
stick together
root pressure: pressure exerted on water in
the roots by osmosis
capillary action: the movement of a liquid
along the surface of a solid
sink: a place in a plant where products of
photosynthesis are stored
cohesion: the tendency of like molecules to
stick together
source: a place in a plant where products of
photosynthesis are manufactured
plasmolysis: the shrinking of the cytoplasm
and the cell membrane away from the cell
wall due to the outflow of water from the
cell
tonicity: a term that relates the concentration
of solute particles in solutions separated
by a semi-permeable membrane
pressure-flow theory: an explanation of
how plant nutrients are transported from
leaves to other parts of the plant, driven by
pressure built up by hypertonic solutions
in the phloem
transpiration pull: a pull on water molecules
in xylem due to the evaporation of water
through stomata and lenticels
Suggested Answers
1. Cell membranes, vacuoles, and vascular tissues are involved in the movement of water and other
materials in plants.
2. Textbook questions 1 to 5 of “Questions,” p. 315
1. Answers will vary. If you were able to use a dropper, you may have been able to get about 40
drops to stay on the penny. If you used your finger as a dropper, you may have been able to
get 60–70 drops to stay on the penny since the drops off the finger are smaller. Was it more
drops than you expected? Did you notice that the water makes a high spot in the centre?
2. When the liquid dish detergent was added, the water ran off. Yes, one or two more drops
could have probably been added.
3. The coloured water moved up the most in the capillary tube with the smallest diameter.
4. The narrower the capillary tube, the further the coloured water travels up the tube.
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131
5. After the stem was cut, the roots continue to absorb water and cause water to move up the
stem. The water did not drain back down into the roots because the water molecules were
clinging to one another and to the sides of the vascular tissues in the stem.
3. Cohesion is the tendency of molecules of the same kind to stick together.
4. Adhesion is the tendency of unlike molecules to stick together.
5. No, plants would not be able to draw soapy water up the stem because the adhesion of soapy
water to the sides of the vascular tubes would not be as great as with plain water.
6. In the early morning, you can see droplets of water on the tips of leaves. This is evidence that
water is being forced through the plant even though the rate of transpiration is low.
7. Water is drawn into the roots through osmosis.
8. When water evaporates from the leaves, a pull on the water inside the leaves and stem is
created.
9. The higher the temperature, the more evaporation and, therefore, the stronger the transpiration
pull. This moves water more quickly through the stem.
10. Textbook questions 1 to 4 of a “Minds On . . . Colourful Carnations,” p. 317
1. In the carnation, the coloured water moved up the stem and into the flower. Each colour
moves only into its half of the carnation. In the celery stalk, the colour moved up mostly
in tubes around the outer edge.
2. You can infer that water moves up the stem through the tubes only. It does not spread
throughout the plant.
3. The cells that are stained are the vascular tissue cells. Other cells appear to be slightly
coloured, but this could be due to osmosis through the cell membranes.
4. The vascular bundles work like capillary tubes. The water adheres to the sides of the
vascular tissue and water molecules cling to each other by cohesion. This adhesion and
cohesion slowly moves the water up the stems.
11. a. In the root system, water is moved from the soil into the roots by osmosis. It is then moved
toward the stem by root pressure.
b. In the stem, water is moved by root pressure and transpiration with the help of the forces of
adhesion and cohesion.
c. In the leaves, water is moved through transpiration pull and by diffusion through the air
spaces.
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12. Predictions may vary. A sample prediction is given.
An environment of increased tonicity will cause water to move out of the cell.
13. a. Diagrams should be similar to the following.
Field of View at 400x
Elodea leaf cell
chloroplast
Diameter of field of view at 40¥ = 4.5 mm
Diameter of field of view at 400 ¥ = 40 ¥ ¥ 4.5 mm
400 ¥
= 0.45 mm
Estimated size of Elodea leaf cell = 1 of field of view
3
Actual size of Elodea leaf cell = 1 ¥ 0.45 mm
3
= 0.15 mm
= 150 mm
The actual size of the Elodea leaf cell is 150 μm.
b. You should be able to see the movement of chloroplasts, particularly around the edges of
the cell.
c. The vacuole shrinks in size and movement within the cell slows down as water moves out
of the cell.
14. a. Textbook questions 1 to 4 of “Analyzing and Interpreting,” p. 319
1. You should see the movement of chloroplasts, especially around the edges of the cell.
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2. Over time, the central vacuole shrinks in size and there is more room for chloroplasts.
Movement slows down as water moves out of the cell due to evaporation from the heat
of the microscope light. The variable responsible for the relationship is time.
3. Adding the salt solution made the surrounding environment hypertonic to the cell contents.
4. The hypertonic environment causes the water to move out of the cell. The water in the
vacuole moves out and the vacuole shrinks in size. As the entire cell loses its turgidity
(firmness of cell wall), you may observe the cell wall shrivel.
b. Textbook question 5 of “Forming Conclusions,” p. 319
5. The vacuole shrinks in size, and the entire cell wall loses its turgidity. The mechanism
responsible is the movement of water across the cell membrane and out of the cell by
osmosis.
15. Refer to the answer to question 13.a.
16. The chloroplasts move around the cell, particularly along the edge of the cell wall.
17. a. The leaf was quite firm and kept its shape when it was cut from the plant. After immersing
it in the salt solution, the leaf became limp and curled.
b. The salt solution caused the water in the cells to move out into the salt solution, reducing
the turgidity of the cells in the leaf.
18. The salt solution is hypertonic to the leaf’s cell contents.
19. a. Plasmolysis is the shrinking of cells when the environment outside the cell has a higher
solute concentration than inside the cell.
b. Plasmolysis causes the leaf of a plant to become wilted or limp.
20. Water re-enters the plant, and the plant regains its turgidity.
21. Turgidity is important in green plants because it holds the green parts of the plants up to the
sunlight.
22. The xylem and phloem are part of the transport system. The xylem brings water up to the leaves
from the roots, and the phloem brings sugar and water down from the leaves to the remainder of
the plant.
23. The leaves where the sugars are manufactured are called the source. The rest of the plant where
the sugars are used or stored is called the sink.
24. The sugars move into the phloem through active transport, and water moves into the phloem by
osmosis. This increases the pressure in the phloem and pushes the water and sugar through the
phloem and into the rest of the plant.
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25. The sugars are used for growth and respiration or may be stored in roots, stems, fruit, and leaves.
26. The constant flow of sugar and water in the phloem is maintained through pressure differences
produced by active transport and osmosis. As sugar and water move down the phloem and into the
cells, a reduced pressure is created in the sink. This forces more sugar and water to move into the
phloem from the source.
27. Textbook questions 1, 2, 3, and 9 of “Check and Reflect,” p. 322
1. The properties of water that aid in water transport in plants are adhesion and cohesion.
2. In a hypertonic solution, water inside the cell and inside the vacuole will move through the
cell membrane to the outside of the cell. This will cause the vacuole to shrink. In a hypotonic
solution, water from outside the cell will move through the cell membrane to the inside of the
cell and into the vacuole. This will cause the vacuole to swell.
3. Plants use the stomata to control water loss. When evaporation rates are high, the stomata will
close to reduce water loss. In the long term, plants that have adapted to dry conditions have few
stomata and have a waxy covering on the leaves (if they have leaves) and stem.
9. Answers will vary. A sample concept map is given.
transpiration
stomata
ground tissue
xylem
phloem
root epidermis
roots
root hairs
Image Credits
All images in this lesson were created by or for Alberta Education with the following noted exceptions:
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129 Copyright © 2005 Alberta Education and its licensors. All rights reserved.
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